To edit your list's footer information.
Go to: Admin > [Non-digest options] and scroll down to:
Footer added to mail sent to regular list members
Edit the following to match your list and enter into the text box:
To unsubscribe from this list, send a blank email to: firstname.lastname@example.org
The repeat the process for Digests: Go to: Admin > [Digest options]
The member will receive a confirmation email containing a link to click to complete their unsubscription.